Alkaline phosphatase, often abbreviated to ALP, is an enzyme found mostly in liver and bone. Abnormal levels of ALP are usually elevations, although low levels of ALP occur in some conditions. ALP is measured as part of the liver function tests or chemistry panel on blood tests. Abnormal ALP levels are not diagnostic for any one specific disease.
Normal ALP Levels
The normal range of ALP is 44 to 147 International Units per liter (IU/L), according to Medline Plus. Fasting for eight hours before the test is preferable because ALP levels may be slightly elevated for several hours after eating.
Causes of Abnormal Results
Many diseases and drugs can cause abnormal ALP levels. Elevated levels occur in liver or bone disease. Liver diseases that raise ALP include blockage in the bile ducts, hepatitis, liver damage and liver cancer. Any type of rapid bone growth can cause elevated ALP levels, including certain bone cancers, healing fractures, osteomalacia, Paget's disease and rickets, according to Jeremy Kaslow, M.D.
Low levels of ALP can occur after blood transfusion or heart surgery, and in people who are malnourished or who have protein deficiency. According to Medline Plus, many drugs also affect ALP levels, including birth control pills, narcotic medications, tranquilizers, antidepressants and anti-inflammatory medications.
Symptoms of Specific Diseases
If liver disease is the cause of an elevated ALP, symptoms might include jaundice, fatigue, decreased appetite, nausea, itching or abdominal pain. Elevated ALP from bone disease may cause bone pain, increased bone fractures or bone deformities, according to Lab Tests Online.
Comparison to Other Lab Tests
Comparing ALP levels to other lab tests can sometimes give a better idea of what's causing the elevated levels. When compared to other liver enzymes, ALP is usually less elevated than AST and ALT--two other commonly tested liver enzymes--if a person has hepatitis and more elevated than other liver enzymes if bile duct blockage is the cause of liver dysfunction. Bone disease causes abnormal calcium and phosphorus in addition to an elevated ALP level.
Considerations
Abnormal ALP levels occur in potentially serious diseases, and should be investigated when they are detected.
